JP-B No. 51489/1987, JP-B No. 51491/1987, JP-B No. 66373/1992, U.S. Pat. No. 4,580,855, etc. disclose solid electrolyte capacitors which comprise a capacitor element including a metal member and impregnated with a TCNQ complex salt as an electrolyte, the metal member acting as a valve and being formed with a chemical conversion coating. "TCNQ" stands for 7,7,8,8-tetracyanoquinodimethane.
FIG. 13 shows one type of solid electrolyte capacitor which is already known and has a bottomed tubular aluminum case 9 housing a capacitor element 1, filled with an epoxy resin 91 and having its opening sealed off.
As shown in FIG. 14, the capacitor element 1 comprises an anode foil 11 which is an etched aluminum foil formed with a chemical conversion coating, and a cathode foil 12 opposed to and superposed on the anode foil 11 with a separator 13 interposed therebetween. The capacitor element is prepared by winding up the assembly of the foils and separator into a roll, and impregnating the roll with a solid electrolyte such as a TCNQ complex salt.
A pair of lead terminals 14, 14 are joined to the anode foil 11 and the cathode foil 12 and have lead wires 15, 15 extending therefrom.
The solid electrolyte capacitor described is fabricated by filling a suitable amount of powder of TCNQ salt into a case 9 first, heating the case at 250 to 350.degree. C. to melt the salt into a liquid, immersing the roll into the molten salt to impregnate the roll with the salt, thereafter rapidly cooling the roll as placed in the case to solidify the salt and finally filling an epoxy resin 91 into the case 9.
Further attention has been directed to solid electrolyte capacitors which are compact, have a great capacity and are small in equivalent series resistance (hereinafter referred to as "ESR") and in which an electrically conductive polymer, such as polypyrrole, polythiophene, polyfuran or polyaniline, is used as a cathode material.
Like the structure shown in FIG. 14, the solid electrolyte capacitor of this type is prepared by winding an assembly of anode foil 11 formed with a chemical conversion coating, cathode foil 12 and interposed separator 13 into a roll, forming an electrically conductive polymer layer in the roll to obtain a capacitor element 1, housing the capacitor element 1 in a case .9 and filling an epoxy resin 91 into an opening portion of the case for sealing as seen in FIG. 13.
The prior-art solid electrolyte capacitors described have the problem of impaired reliability involving variations in capacitance and increases in ESR due to the degradation of the sealing epoxy resin or the penetration of moisture through the portion of contact between the sealing epoxy resin and the case or through the portion of contact between the sealing epoxy resin and the lead wire.
The solid electrolyte capacitor wherein the conductive polymer is used as a cathode material has another problem. Before the epoxy resin poured in for sealing cures, a component of the resin penetrates into the capacitor element to lower the electric conductivity of the polymer to result in increased ESR, or the thermal stresses involved in the pouring and curing of the epoxy resin cause damage to the chemical conversion coating on the anode foil of the capacitor element to increase the leakage current (hereinafter referred to as "LC").